An endoscopic system of this type is known from patent application JP-2005-205195.
Endoscopes and microscopes constitute in medicine, by now, an indispensable aid for certain diagnostic and therapeutic questions. In particular, in the context of minimally invasive surgery they make possible a mild alternative to conventional open surgery. The brightest possible illumination of the examination area is an urgent necessity in exploring the examination area, which normally is completely dark, with the help of the observation system of an endoscope, which can take the form of a classical relay-lens system, a fiber image conductor, or an electronic image sensor chip (CMOS, CCD) for video image reception
In addition to their use in human or veterinary medicine, endoscopic or microscopic examinations have proven themselves as well in technical areas, such as for examining hollow cavities in turbines and engines. Even in these applications, good illumination of the area of investigation can be indispensable for an accurate depiction by the observation system of the endoscope, and should also provide a quantitative measure of fissure lengths.
The examination area is normally illuminated by a light conductor with a small cross-section, consisting of an optic fiber or a fiber bundle by which light is conducted from an external light source into the examination area.
The light source must therefore convey light with a high capacity or capacity density, in order to ensure sufficient illumination of the hollow areas.
For this purpose, arc lamps such as high-pressure xenon short-arc lamps are generally used. These arc lamps radiate incoherent light, which in some cases is imaged or focused onto the light entry end of the optic fibers or of the fiber bundle by means of an appropriate diaphragm or lens system.
Increasingly, however, light diodes and lasers, in particular laser diodes (LD), are coming into use. Laser diodes comprise higher light densities than light arc lamps. Laser light sources, in addition, have a long lifetime. Laser light can be easily transmitted by thin probes and cables.
Among possible laser light sources for endoscopes and OP microscopes are laser-pumped fluorescent light sources, continually modulated or pulsed (IR) lasers, blue or UV lasers for fluorescent excitation, continually modulated or pulsed blue or UV lasers, RGB/RGBA white light laser light sources, supercontinuum white light laser sources, or IR lasers.
The light that is usually emitted by a laser comprises narrow spectral bands. Because of this spectral purity, laser light can preferably be used, in particular, for fluorescent excitations, because this makes it easy to filter out the excitation light. For color reproduction, however, it is optimal to use a white illuminating light with a spectral characteristic as close as possible to a black body radiance.
In patent application JP 2005-205195, therefore, a fluorescence converter is positioned in the illuminating beam path to generate white light, on the additive color mixing principle, from the blue excitation light of a laser and the yellow light portions arising in a fluorescence converter. The light radiated from an LED or a laser diode (LD) in the blue spectral range is fed by a condenser device into a thin multimode glass fiber. The other end of the glass fiber is equipped with a wavelength transformer element. This element consists of an output portion on the end of the glass fiber, which is encased with fluorescent material. Because of the white light generation concentrated on the distal end of the glass fiber, the embodiment is especially suited for endoscopic applications. By selecting the laser emission wavelengths and the composition of the fluorescent material, a range of color shades is possible in the fluorescence conversion and color mixing.
The radiated light from lasers is coherent because of the process of its production, whereas the fluorescent light emitted by the fluorescent body because of the excitation with laser light is incoherent.
The fluorescence converter is also called a fluorescent body in order to emphasize its property as a diffuser body that diffuses the passed-through excitation light in all spatial directions. The diffusion occurs because of the diffuser centers mounted in the volume of the fluorescent body and because of structural effects on the surface. Here the diffuser centers can at the same time also be fluorophores. Because of their dimensions, the diffuser centers selectively can preferably diffuse the short wavelengths.
Because of the illumination of a surface with at least partial coherent light, so-called speckle patterns can develop on the illuminated area, which can be seen in images of the illuminated area taken with a video camera.
The speckles are frequently characterized by a granular, bumpy or sandpaper-type texture. The appearance of a speckle can resemble a surface that is sprinkled with fine particles.
The formation of speckles is less conspicuous and disturbing with moveable, hand-held endoscopic instruments than with stationary instruments or systems, for instance an operation microscope. Because of the stationary, immobile position of the operation microscope or of the target object, the speckles are not transmitted temporally by any hand-shaking motion (tremor) and thus are substantially more recognizable. Thus, also with OP microscopes in addition to the aforementioned endoscopes, a reduction of the speckles is very important.
U.S. Pat. No. 4,011,403A discloses a laser-illumination and observation system in which means are available for periodic excitation of the system for purposes of speckles reduction.
Reducing the speckle pattern is indispensable for a reliable evaluation of the image information. Thus, for instance in industrial applications like the inspection of hollow engine spaces, the apparently rough texture of the speckle artifacts can be mistaken for corrosion, impurities, or deposits.
In medical applications, confusion of the speckle pattern with the appearance of lesions, for instance, could lead to misdiagnoses in medical examinations.
It is consequently the task of this invention to further develop an endoscopic or microscopic system of the aforementioned type so that it efficiently provides an illumination of the examination area that is as free as possible of speckles.